The present invention relates to disk storage apparatus and particularly to apparatus employing data recorded in the disk in a specific format.
Rotating magnetic storage disks have become quite popular in the data processing industry for storing large amounts of data and still having it relatively directly accessible on a random basis. Such disks have employed so-called "rigid" disks wherein a comb-shaped head support assembly moves radially in and out of an axial stack of such rigid disks. One of the disks is a servo-positioning disk, which determines the location of all tracks in all of the remaining disks which store data signals. One difficulty with such an arrangement is that the volumetric efficiency and cost come extremely high as the amount of data stored increases.
It is well known that flexible record media is much less expensive than rigid record media. Additionally, a flexible record disk can be stacked closer together, the apparatus could replace rigid disk packs resulting in a greater volumetric efficiency. An example of a disk storage apparatus employing a stack of flexible, rotatable, storage disks with independent access to each of the disks is shown by Raymond A. Barbeau et al in U.S. Pat. No. 3,852,820. The present invention is advantageously employed with such apparatus, as will become apparent, no limitation thereto intended.
As the recording density on rigid disks increases beyond that presently found in such record storage apparatus, some of the tolerance problems associated with track following, i.e., keeping a transducer centered over a record track, accessing tracks (selecting which track to transduce), and generally achieve reliable recording and readback, are solved by this invention and are applicable to rigid disk apparatus for solving problems of run-out, accurate track positioning, and other associated problems. Prior solutions to some of these have included zoning the disk record surface into radial bands such that the bit packing density for a given frequency of data transfer does not vary excessively from the outer radii to the inner radii of each zone. The data transfer rate varies from zone to zone--typically a 2-to-1 difference between innermost and outermost zones. This difference requires channels of different bandwidth. However, system problems, i.e., computer programming problems, associated with different length records, appear to have limited application of such banding. Additionally, banding has been known to provide for adaptive equalization of the readback signal. That is, equalization techniques for each band are automatically switched in accordance with the speed of the recording surface with respect to a sensing transducer.
Virtual memory mass store systems have advantageously employed fixed block lengths for facilitating space management and addressing techniques. Most data sets in common use have a variable length; hence, the program in virtual memory systems accommodates the variable block length to various techniques beyond the scope of the present specification. However, in managing storage space for use with virtual memory systems, a fixed block length has certain advantages.